Depends on the subject of the documentary. I watch many of them on various subjects. I love to learn and explore things that I would love to do myself, or places I would like to visit, or subjects that I want to know more about.
Not really. I have a very narrow range of interests and an even smaller attention span. Every once in a while i can last out a TED talk but not usually a documentary, particularly if they are inclined toward reenactments of events. I don't do much better with entertainment movies either.
I like documentaries on subjects in which I have an interest, or might not know much about. Inquiring minds want to know.